Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.
The formation of in ground granular stone columns can be accomplished by a number of means, one means uses a drill which includes an auger within a hollow tube. When the drill is at the desired depth the aggregate is fed into the centre of the hollow tube and the auger rotated to form the granular stone column. As the aggregate is a granular material it can bridge and partially or completely block the flow of aggregate into the stone column. To overcome this bridging it is possible to manually clear this bridging but this can be time consuming and can affect the quality of the granular stone column formed.
To minimise bridging and allow the drill to be more easily extracted from the ground as the granular stone column is formed the auger can be driven in the opposite direction to the hollow tube. One method proposed for this uses an epicyclic gear, with the auger permanently attached to the sun gear and the annulus (annular gear) driven. In some variations, to prevent the auger being continuously driven, the sun gear is disengaged from the planetary gears. If the sun gear is disengaged during the initial drilling it needs to be properly aligned then engaged with the planetary gears before the granular column can be formed, this can be time consuming and if misaligned with power applied it could damage or break the teeth or gears. It should be noted that the reverse direction of the auger and the hollow tube still bridges, this bridging then needs to be cleared before continuing.
In addition to the bridging problems that can increase the time taken to prepare a granular stone column there is also a need to compact the aggregate during formation of granular stone column. The feed rate of aggregate, rpm of the drills and extraction rate of the drill from the ground can all be varied, but even then it can be difficult to achieve the required compaction. To improve compaction the completed stone column can be mechanically vibrated, but this is an additional step.
In some ground environments the drill can ‘stick’ during extraction which can increase the time taken to form each granular stone column, or in some cases require additional machinery to clear.
It is an object of this invention to overcome or mitigate one or more of the deficiencies highlighted above, and/or to at least provide the consumer with a useful choice.